The present invention relates to a power supplying apparatus for supplying electric power to heating elements which heat various parts of an automobile and the like. More particularly, it relates to such a power supplying apparatus which is capable of preventing wasteful power consumption upon a failure such as short-circuiting in the heating elements.
In general, automotive parts are equipped with various heating elements which are supplied with electric power from a common power source in the form of a battery.
For example, when the temperature of intake air sucked into cylinders of an internal combustion engine is low, ignition of the intake air becomes rather difficult, so it is necessary to heat intake air for ensuring good ignition. In particular, with diesel engines, ignition becomes very difficult at the time of engine starting. To improve this situation, a heating element such as a glow heater is required. Also, a wind heater is used for defrosting the front windshield and the like of an automotive vehicle. Further, in cold weather, the function of a catalytic converter, which treats and purifies exhaust emissions from an internal combustion engine, is reduced or degraded due to low temperatures, so in this case, a heater is required to heat the catalytic converter.
The power consumption of these various kinds of heating elements usually reaches a maximum of several kilo watts. Thus, considering that the source voltage of a battery for automotive use is generally 12 volts, current of about 400 amperes is required, thus imposing a high load on the battery.
FIG. 14 illustrates in block form a typical example of a power supplying apparatus for supplying electric power to various kinds of automotive heating elements. In this figure, the apparatus illustrated includes an AC generator in the form of an alternator 1 having a rectifier incorporated therein, and a battery 2 adapted to be charged by the alternator 1. The AC generator 1 is operatively connected with an unillustrated engine so that it is driven to rotate by the engine. The alternator 1 and the battery 2 together constitute a source of electricity for supplying electric power to a heating element In the form of an electric heater 3.
The heater 3 can be mounted on an automotive part such as a catalytic converter and the like for heating it. The heater 3 is electrically connected to a junction between the alternator 1 and the battery 2. A temperature sensor 4 is provided for sensing the temperature of the heating element, i.e., the ambient temperature of the heater 3. A control switch 5 is connected at one end thereof to the heater 3 and at the other end to ground for selectively switching on and off the power supply to the heater 3. A control circuit 6 is connected to the temperature sensor 4 and the control switch 5 for generating a control signal C to the control switch 5 based on an output signal T from the temperature sensor 4. Though not illustrated, a drive circuit is connected between the control circuit 6 and the control switch 5 for generating an operation voltage for the switch 5 based on the output voltage of the power supplying means in response to the control signal C from the control circuit 6.
The operation of this apparatus will now be described below. First, during normal operation of the engine, the alternator 1 is driven to rotate by the engine and generate electric power, e.g., three-phase AC voltage, which is converted by the built-in rectifier into a DC voltage of an appropriate value, e.g., 12 volts. The DC voltage is then output from the alternator 1 to the battery 2.
If the temperature of the unillustrated automotive part such as a catalytic converter goes low for some reason during operation or non-operation (stoppage) of the engine, the temperature sensor 4 senses such a situation and generates an output signal T indicative of the fact that the sensed temperature is below a predetermined lower limit. In this case, in response to the output signal T from the temperature sensor 4, the control circuit 6 generates a control signal C for closing or turning on the control switch 5. As a result, the heater 3 is supplied with electric power from the power source, i.e., from the alternator 1 and the battery 2, thereby properly heating the catalytic converter to a temperature above the predetermined lower limit. After the lapse of a predetermined time at which a sufficient rise in the temperature of the catalytic converter is expected, the control circuit 6 opens or turns off the control switch 5, thus cutting off the power supply to the heater 3. In this manner, the intended function or performance of the catalytic converter can be ensured.
In this regard, the suitable temperature of the catalytic converter at which catalyst therein is effective to function usually ranges from 350.degree. C. to 400.degree. C., and the temperature of exhaust gases during engine operation is at about 600.degree. C. Accordingly, the power supply to the heater 3 is carried out only for a short time during cold engine starting.
However, when electric power is supplied to the heater 3, the output voltage of the battery 2 gradually falls and finally gets short of a minimum voltage required for normal operation of the engine. As a result, the output torque of the engine may be accordingly decreasing, thus resulting in reduction in the running performance and acceleration performance. In particular, since the engine load becomes high at the time of engine starting, if the power supply to the heater 3 is effected prior to engine starting, the battery is excessively exhausted, making it difficult or impossible to start the engine, or reducing the running and acceleration performance. In addition, the charging capability of the alternator 1 and the rechargeable capacity of the battery 2 are limited, so the recovery time of the battery 2 (i.e., the time required for charging the battery 2 to the initial or fully charged level) increases.
In particular, after aging degradation and excessive discharge of the battery 2 or in the cold state of the battery 2, the rechargeable capacity of the battery 2 degrades, so the battery 2 takes a lot of time for recovery.
Moreover, in the event that the catalytic converter is at a remarkably low temperature, it will take a long time to sufficiently heat the catalytic converter to a temperature above a certain activation temperature level with use of the battery 2 alone. Still further, in order to supply a desired amount of electric power (i.e., several kilowatts) to the heater 3, a large current (e.g., current of about 400 amperes for the battery voltage of 12 volts) is needed, so the required current ratings for the control switch 5 and wiring accordingly increase.
Since the control switch 5 is turned off after the lower limit temperature for the catalytic converter is reached, if the atmospheric temperature is very low, the temperature of the catalytic converter rapidly falls below the lower limit immediately after the power supply to the heater 3 has been cut off, thus resulting in frequent on/off operations of the control switch 5.
Moreover, upon start of the power supply to the heater 3, the voltage of the battery 2 momentarily falls. Therefore, particularly in cases where the capacity of the battery 2 is low due, for example, to excessive discharge and the like, the battery 2 may have an output voltage less than a threshold voltage which is required for driving the control switch 5 on and off in response to a control signal C from the control circuit 6, thus leaving the control switch 5 in the off mode.
Furthermore, during engine cranking in the engine start-up operation, the engine load becomes high so that it power is simultaneously supplied to the heater 3 and an engine control system, the output voltage of the battery 2 abnormally falls, thus giving rise to a fear that the engine can not be successfully started up.
On the other hand, if the heater 3 has been short-circuited, e.g., grounded due to some trouble, power is continuously supplied to the heater 3 irrespective of the on or off condition of the control switch 5, thus resulting in useless consumption of electric power.